Eugene L. Birch of the Brookings Institution just completed an analysis of population, household and income trends in downtown areas from 1970 to 2000 called Who Lives Downtown 
Download full the report [pdf] 
The study was based on 44 different cities whose results vary widely but show these trends:
During the 1990s, downtown population grew by 10 percent, a marked resurgence following 20 years of overall decline.
From 1970 to 2000, the number of downtown households increased 8 percent—13 percent in the 1990s alone—and their composition shifted.
Downtown homeownership rates more than doubled during the thirty-year period, reaching 22 percent by 2000.
Downtowns are more racially and ethnically diverse than 20 years ago.
In general, downtowns boast a higher percentage of both young adults and college-educated residents than the nation’s cities and suburbs.
Downtowns are home to some of the most and least affluent households of their cities and regions.
The results, if based on the past five years would likely show a more pronounced shift toward urban revitalization.